1. Field of the Invention
The present invention relates to a high SAG optical lens and method for fast molding the same; in particular, it relates to an optical lens having a formed rim structure which is fabricated through glass molding or plastic molding process. The optical lens can be used for the optical zoom lens of a camera or of an optical system.
2. Description of Prior Art
The technologies of glass precision molding or plastic precision molding have been comprehensively applied to making aspheric molding glass (plastic) lens, which is characterized in high resolution, excellent stability and competitive manufacture cost, such as those disclosed in US2006/0107695, US2007/0043463, Taiwan Patent TW095101830, TW095133807, Japan Patent JP63-295448 and the like. They use the feature of glass (plastic) melted at high glass transition temperature, in which a glass preform or a plastic resin is placed into a mold cavity constituted by the upper mold and the lower mold, for heating and softening. Then the upper mold core and the lower mold core are closed and clamped for pressing, such that the mold surfaces are transferred onto the softened glass preform (or plastic resin). After cooling, the upper mold core and the lower mold core are separated to obtain the optical lens product with optical surfaces by transferring the upper and lower mold cores. Refer first to FIG. 1, a glass or plastic material 4 is placed into a mold cavity which is formed between an upper mold 951 and a lower mold 952, and is heated to exceed its glass inversion point, allowing the glass or plastic material 4 to be in a softened or melted state. The upper mold 951 and the lower mold 952 are respectively configured with a forming surfaces of the optical surfaces, and they can apply pressure and cast the softened glass or plastic material when they are closed and clamped, thus forming an optical lens 91, such that the forming surfaces of the upper mold 951 and the lower mold 952 are transferred onto the optical lens 91, accordingly creating two optical surfaces on the optical lens 91. However, for the curved surface of greater curvature radius, the altitude of optical lens is smaller (low SAG) and the molding process is simpler; whereas in terms of surface with smaller curvature radius, the altitude of optical lens may be greater (high SAG), the molding process thereof thus becomes more challenging.
In conventional moldings, to deal with the optical surface having a complicated structure or high SAG, it is usual to take the approach of heating process in order to soften the glass or plastic material 4, thus increasing the liquidity and decreasing the viscosity by using higher molding temperature thereof to facilitate the molding process. However, such an approach may cause drawbacks such as prolonged manufacture period or undesirable molding stickiness. An alternative approach is stacking a higher SAG optical lens, such as disclosure in Japan Patent JP2006-337985 and US Patent US20070091443, which is using the UV plastic and configure a multi-layer structure on the molding tools to mold an optical lens array. In order to achieve precision molding, to solve the problems of lithographic in the glass or plastic material 4 and the mold cavity, another conventional approach is to draw out air from the mold cavity for reaching a vacuum status, thereby preventing occurrences of air gaps in the mold cavity adversely affecting the formation of the optical surface. Nevertheless, such a solution may cause disadvantages in extra manufacture cost and slow process speed. Besides, the disclosures of Japan Patent JP2002-003225, JP05-286730, JP06-191861, US Patent US2005/0172671, EU Patent EP0648712 and Taiwan Patent TW I256378 attempt to resolve the problem of air residue by adjusting pressure, temperature or surface roughness and so forth to control operational conditions. Moreover, the disclosures of Japan Patent JP61-291424, JP2000-044260, Taiwan Patent TWI248919, TW200640807, US Patent US2005/0242454, and the like propose air tunnels configured in the molding equipments as the outlets for air expulsion; or otherwise, in the disclosures of Japan Patent JP61-291424, JP08-337428, JP2009-046338, JP2001-033611, U.S. Pat. No. 7,159,420 etc., grooves or air outlets are installed on the molding tools for removing the air. Now refer to FIG. 2, grooves 9514 are randomly configured on a flange transfer surface 9512 of a non-optical surface along the flange of an upper transfer surface 9513 in the optical surface of the upper mold 951; upon molding, air can be released through the groove 9514. Referring to FIG. 3, a groove transfer surface 9533 is configured on the lower transfer surface 9523 in the optical surface of the lower mold 952. However, such grooves or air outlets may correspondingly create bumps on the molded lenses, causing problems of requirements on secondary machining or difficulties in subsequent assemblage.
The lens flange of the optical lens is an optically inactive zone; for example, U.S. Pat. No. 7,349,161 and U.S. Pat. No. 7,540,982 use the lens flange to install an indentation for measuring eccentricity. Refer to FIG. 4, wherein an indentation 914 is grooved on the lens flange 912 of the optical lens 91 and the optical surface 910, and an alignment 9141 is configured in the groove 914, in which the alignment 9141 and the optical lens 91 are concentric thereby using the alignment 9141 for the purpose of eccentricity measurement.
Refer to FIG. 9(A), in which the optical surface 12 of the optical lens 1 is able to refract the incident light Li through the optical surface 12 and forms an ejected light Lo focusing on a spot, thereby achieve the optical effect of the optical lens 1. However, due to various mold machining limitations and molding procedures, a buffer surface 15 is formed adjacent to the lens flange 11 and the optical surface 12 in the optical lens 1. The buffer surface 15 is characterized in an arc-shape surface, with a curvature radius of Rc, so the buffer surface 15 may act as a converging concave lens allowing the incident light Li′ to change path into the ejected light Lo′; and further because of the curvature radius of Rc, the ejected light Lo′ is converged into a concentrated light beam so that a ghost image is formed. Such a problem may frequently occur in the optical lens of high SAG surface.
Therefore, regards to the optical lens of high SAG surface, a feasible solution is imminently needed for effectively reducing manufacture cost, facilitating molding process and also preventing the ghost image.